From: James Chapman <jchapman@katalix.com>
To: Mandeep Singh Baines <mandeep.baines@gmail.com>
Cc: netdev@vger.kernel.org, hadi@cyberus.ca, davem@davemloft.net,
jeff@garzik.org, ossthema@de.ibm.com,
Stephen Hemminger <shemminger@osdl.org>
Subject: Re: RFC: possible NAPI improvements to reduce interrupt rates for low traffic rates
Date: Mon, 10 Sep 2007 10:33:34 +0100 [thread overview]
Message-ID: <46E50F6E.5010503@katalix.com> (raw)
In-Reply-To: <20070908164222.GB3765@ludhiana>
Mandeep Singh Baines wrote:
>> Why would using a timer to hold off the napi_complete() rather than
>> jiffy count limit the polls per packet to 2?
>>
> I was thinking a timer could be used in the way suggested in Jamal's
> paper. The driver would do nothing (park) until the timer expires. So
> there would be no calls to poll for the duration of the timer. Hence,
> this approach would add extra latency not present in a jiffy polling
> approach.
Ah, ok. I wasn't planning to test timer-driven polling. :)
>> Why wouldn't it be efficient? It would usually be done by reading an
>> "interrupt pending" register.
>>
> Reading the "interrupt pending" register would require an MMIO read.
> MMIO reads are very expensive. In some systems the latency of an MMIO
> read can be 1000x that of an L1 cache access.
Agreed. Testing for any work being available should be as efficient as
possible and would be driver specific.
--
James Chapman
Katalix Systems Ltd
http://www.katalix.com
Catalysts for your Embedded Linux software development
next prev parent reply other threads:[~2007-09-10 9:33 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-09-06 14:16 RFC: possible NAPI improvements to reduce interrupt rates for low traffic rates James Chapman
2007-09-06 14:37 ` Stephen Hemminger
2007-09-06 15:30 ` James Chapman
2007-09-06 15:37 ` Stephen Hemminger
2007-09-06 16:07 ` James Chapman
2007-09-06 23:06 ` jamal
2007-09-07 9:31 ` James Chapman
2007-09-07 13:22 ` jamal
2007-09-10 9:20 ` James Chapman
2007-09-10 12:27 ` jamal
2007-09-12 7:04 ` Bill Fink
2007-09-12 12:12 ` jamal
2007-09-12 13:50 ` James Chapman
2007-09-12 14:02 ` Stephen Hemminger
2007-09-12 16:26 ` James Chapman
2007-09-12 16:47 ` Mandeep Baines
2007-09-13 6:57 ` David Miller
2007-09-14 13:14 ` jamal
2007-09-07 21:20 ` Jason Lunz
2007-09-10 9:25 ` James Chapman
2007-09-07 3:55 ` Mandeep Singh Baines
2007-09-07 9:38 ` James Chapman
2007-09-08 16:42 ` Mandeep Singh Baines
2007-09-10 9:33 ` James Chapman [this message]
2007-09-10 12:12 ` jamal
2007-09-08 16:32 ` Andi Kleen
2007-09-10 9:25 ` James Chapman
2007-09-12 15:12 ` David Miller
2007-09-12 16:39 ` James Chapman
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